Most data storage and retrieval is done by use of magnetic recording apparatus, mainly disc drives and tape drives (the term "drive" having come to be accepted as the basic industry designator for recorder/reproducer devices). In the case of disc drives, there are both "hard" disc and "floppy" disc-type media, the "hard" disc being a rigid platter having a magnetizable surface upon which magnetic flux transitions are recorded by means of a transducer head which aerodynamically "flies" with respect to the surface of the disc, being spaced therefrom by a thin film of air. "Floppy" disc drives utilize magnetically recordable media which although disc-like in shape is much more in the nature of magnetic tape, being highly flexible and typically comprising a sheet of polymeric material carrying a surface coating of magnetizable metal oxide. In floppy disc drives, as in tape drives, recording is accomplished by maintaining direct contact between the moving media and the recording head, usually by projecting the tIp of the head (at the magnetic "gap") into the plane of the flexible media as it moves past the head.
Tape drives typically, or at least frequently, feature bi-directional recording and reproducing operation in which the tape is transported along its length from one end to the other during a first read or write operation and then transported back in the opposite direction for the next such operation, without rewinding the tape between the two successive recording operations as would usually be done in tape recording. This bi-directional operation is not characteristic in disc drives (whether "floppy" or "hard" disc media is involved), in which the disc-form media is continuously rotated in the same direction and all recording or reproduction on the media is done unidirectionally.
This rather fundamental difference in operational modes creates a corresponding fundamental difference in the nature of the transducers or heads which may be utilized. In the case of bi-directional reading and writing, a multi-gap head is used, but in the case of unidirectional recording only a single-gap head is necessary, which is much less expensive than a multi-gap head but has the disadvantage of only being able to read and write at different times; i.e., it cannot write and simultaneously read data, as is frequently desirable and is often provided for in tape drives.
Furthermore, in order to maximize the likelihood that the read gap will be properly positioned directly over the written track on the media, two essentially opposite approaches have come to be recognized in the art with respect to the multi-gap heads used in tape drives. The first of these involves use of a write gap which is substantially wider than the read gap, such that if the read gap is nominally positioned anywhere near the center of a written track, the head is likely to be fully in registration with the track, i.e., recorded transitions extending across the entire height, i.e. length, of the gap. The second such approach involves use of a head having a separate erase gap disposed ahead of the write gap, so that the media is erased cleanly before each writing operation takes place; thus, the writing is always accomplished on media having no residual signals. In this arrangement, a read gap is used which is considerably wider than the written track, so that the entire width of the written track is always likely to be completely straddled by the read gap. Since the separate erase gap eliminates all residual or extraneous signals recorded contiguous to the narrower written track, interference, cross-talk and the like will not be present in the read data stream.
Since the approaches just described can only be accomplished with multi-gap heads, they are not utilized in floppy disc drives, where only single-gap read/write heads are used. In order to provide a system somewhat analogous to the second arrangement described above, floppy disc drives frequently utilize a "tunnel erase" concept, in which separate erase gaps are provided on both sides of, and to the rear of, the single read/write gap. The function of the two such erase gaps is to "trim" the marginal edges of the written data track by erasing along both sides thereof, thus producing a resultant narrowed track of written data, the sides of which have no residual or extraneous recorded transitions. In this arrangement, the head structure is somewhat complex since it is necessary to space the erase gaps rearwardly of the read/write gap in order to eliminate or minimize both mechanical and magnetic interference problems, and of course there is the added requirement and expense of providing, and assembling, two separate erase gaps.
The tunnel-erase concept just described is not advantageous in bi-directional recording operations, since bi-directional use of that type of head would inherently necessitate the addition of another pair of erase gaps, spaced on the opposite side of the single read/write gap from the location of the first such set of erase gaps, in order to accommodate both of the possible mutually-opposite recording directions. The realities of manufacturing such a head do not favor its potential use, since the required accurate alignment of the various erase gaps with respect to themselves and with respect to the single read/write gap results in a different manufacturing process which inevitably adds substantial expense. Of course, there is also additional expense involved in the requirement of the second pair of erase gaps, in and of themselves.
In an effort to provide a solution for the difficulties and problems discussed above, it has heretofore been proposed to use a different form of core structure for such transducer heads, which in effect provides operational characteristics functionally representative of those typically found in multi-gap heads, while nonetheless having in fact only a single read/write gap.
More particularly, it has been proposed in the past, to use a transducer head whose magnetic core structure has a full-width write core disposed on one side of the gap and a partial-width read core on the opposite side of the gap. In this structure, special additional magnetic closure or return pieces are disposed on opposite sides of the comparatively narrow read core at the gap, to in effect fill the space created by narrowing the read core. These additional components serve as part of the write core structure during write procedures but are not intended to contribute to the read core output signal appearing on a sense coil accessing only the read core. For examples of such transducer core structures, reference is made to Japanese Patent Publication Nos. 50-111817 (Pat. No. 5235618) and 58-171710 (Patent Abstracts Vol. 8, No. 10, P. 248), as well as U.S. Pat. No. 4,085,429.
The last-mentioned of the above disclosures discusses the overriding importance of obtaining the most favorable signal-to-noise ratios possible in using such special-purpose transducers, and of isolating the read channel from the write channel therein, and this prior patent is predicated upon the use of certain allegedly critical limitations for the thickness, with respect to the magnetic gap, of isolation layers proposed for use between the narrowed read core and the special additional write core closures disposed on opposite sides of the read core.
Notwithstanding the factors just noted, the prior efforts of others in the field have until now failed to appreciate and take into consideration certain other highly significant factors involved in the design considerations for the special-purpose transducer-head core structure involved, and the present invention is based upon, and provides, recognition and disclosure of these important factors. Thus, the present invention provides new and valuable structural features and arrangements for such a core structure, involving improvements which are of such importance where high-density recording is involved as to ultimately make the difference between successful and unsuccessful operation, bearing in mind the underlying requirement that in actual operation such a device must be substantially free from spurious error and consistently reliable in performance.
Accordingly, the present invention provides structural improvements and design criteria for "wide-write, narrow-read" magnetic transducer core structures, which improvements make high-density recording operation possible with attendant low error rates. Broadly speaking, the invention provides important structural and size relationships in the elements comprising the magnetic core; more particularly, the invention provides certain critical size relationships in the area of overlap between the read core and the special write core closures which, when carried through in the incorporation of isolation components (laminar elements, at times referred to as "strata"), provide the consumately desirable operational results just noted.
The foregoing generalized features of the invention will become more apparent following due consideration of the ensuing specification and the appended drawings, in which a preferred embodiment is disclosed to illustrate the underlying concepts and the overall aspect of the invention.